I've been playing him for a while for the sheer hilarity of it, so I can only give tips on how to face range spammers like Robin and Megaman; stay on the ground and stick to shielding; in the air, your tactics range only from a down B to some low range air moves, and it makes it too easy to react to you especially since ganondorf can't really move horizontally far at all; force reaction from them by approaching while keeping your shield up, and read them appropriately. This can apply to some other heavyweights aswell.
As for those other low % KO methods being mentioned, only DK's really seems to have any good setup for it, since you can charge up the punch and use it as you please; relying on the slowness of the most powerful attacks of the other bruisers is gonna leave you more exposed than a pigeon rushing to a dropped breadcrumb in a fancy restaurant.